Focal plane mass spectrometers are known. For example, one popular focal plane type mass spectrometer is of the so-called Mattauch-Herzog geometry. These devices spatially separate ions having different masses along the focal plane. An advantage of this kind of spectrometer operation is that 100 percent duty cycle is possible along with the high sensitivity for ion detection. This compares with previous systems such as photographic plates, which may be cumbersome and may lack sensitivity.
An electro-optic ion detector (EOID) is described in U.S. pat. No. 5,801,380 for the simultaneous measurement of ions spatially separated along the focal plane of the mass spectrometer. This device may operate by converting ions to electrons and then to photons. The photons form images of the ion-induced signals. The ions generate electrons by impinging on a microchannel electron multiplier array. The electrons are accelerated to a phosphor-coated fiber-optic plate that generates photon images. These images are detected using a photodetector array.
The EOID, although highly advantageous in many ways, is relatively complicated since it requires multiple conversions. In addition, there may be complications from the necessary use of phosphors, in that they may limit the dynamic range of the detector. A microchannel device may also be complicated, since it may require high-voltage, for example 1 Kv, to be applied. This may also require certain of the structures such as a microchannel device, to be placed in a vacuum environment such as 106 Torr. At these higher pressures of operation, the microchannel device may experience ion feedback and electric discharge. Fringe magnetic fields may affect the electron trajectory. Isotropic phosphorescence emission may also affect the resolution. The resolution of the mass analyzer may be therefore compromised due to these and other effects.
The present application defines a charge sensing system which may be used, for example, in a Mass Spectrometer system, e.g. a GCMS system, with a modified system which allows direct measurement of ions in a mass spectrometer device, without conversion to electrons and photons (e.g., EOID) prior to measurement. An embodiment may use charge coupled device, xe2x80x9cCCDxe2x80x9d technology. This CCD technology may include metal oxide semiconductors. The system may use direct detection and collection of the charged particles using the detector. The detected charged particles form the equivalent of an image charge that directly accumulates in a shift register associated with a part of the CCD. This signal charge can be clocked through the CCD in a conventional way, to a single output amplifier. Since the CCD uses only one charge-to-voltage conversion amplifier for the entire detector, signal gains and offset variation of individual elements in the detector array may be minimized. This may prove to be an advantage over CMOS technology.